Applications exist, such as in motor control, in which it is desirable to have an electronic component that will block relatively high voltages (greater than 50 volts) and pass relatively high current (greater than 100 amps) in either direction. Configurations such as a pair of complementary symmetry conductivity modulated field effect transistors (COMFETs), or a pair of series-connected power MOSFETs, may be used for this purpose. However, these conventional approaches have the disadvantage of requiring multiple semiconductor chips.
In commonly assigned U.S. Pat. No. 4,546,375, VERTICAL IGFET WITH INTERNAL GATE, S. C. Blackstone et al., issued Oct. 8, 1985, an internally gated vertical MOSFET is disclosed. Although it might appear that the enhancement mode embodiment of such a structure would be suitable for relatively high power switching, the device inherently includes certain limitations which significantly limit its operating range. Basically, these limitations occur because of the presence of a relatively high gain parasitic bipolar transistor, the absence of a voltage-supporting semiconductor region (for blocking in each direction) and the relatively low quality of the gate oxide/silicon interface. In an effort to overcome these limitations the structure and fabrication method of the present invention was conceived.